Hydrophilic surroundings requisite for the solubilization of proteins related with their hydrophobicity in the AOT reversed micellar extraction

The reversed micellar extraction (AOT/isooctane system) using the phase transfer method was investigated in relation to the AOT concentration and the water solubilization for ribonuclease A, lysozyme and cytochrome c. The minimal AOT concentration required for 100% forward extraction was obtained for these proteins. At the minimal AOT concentration, the hydrophilic surroundings, i.e. the molar ratio of water to extracted protein in the organic phase, were independent of the protein concentration for each protein. The hydrophilic surroundings of these proteins were linearly related with Fisher's polarity ratio, p, as an index of the hydrophobicity of the protein. Using this linear relation, a procedure to estimate the sufficient AOT concentration for the protein extraction was proposed. In the cases of cytochrome c and lysozyme, the water concentration was larger than that in the protein-free system in spite of the same AOT condition. On the contrary, in the case of ribonuclease A, this large water uptake in the organic phase was not observed. These differences of water uptake were discussed in relation to the location of the protein in the AOT reversed micelles.